The battery has become a primary power source for many portable electronic devices such as radios, hearing aids, watches, calculators, and the like. Many of these electronic devices are designed to operate at a minimum voltage level and therefore require a power source capable of delivering a relatively stable voltage output. Some of the electronic devices, such as watches, are designed to operate from a source of power that can deliver pulse voltage outputs at a stabilized level. It has been observed that nonaqueous lithium cells generally cannot maintain a sufficiently high voltage during the pulsing of the cells thus making them unsuitable in some instances for operating electronic devices such as watches. This problem is believed to be due to the polarization of the lithium anode caused by the presence of a passivating film on the lithium. Thus when the lithium cell is pulsed, the voltage drops until the film is sufficiently disrupted to allow the relatively unimpeded transport of ions to and from the anode. As the current increases due to the increased ion flow, the voltage wil also begin to rise so as to approach a steady state or stabilized level. This delay in achieving a stable voltage on load is most apparent when the cell is pulsed at low temperatures and is also aggravated by open circuit storage at room temperature and above.
Another problem encountered with cells such as nonaqueous lithium cells is that when they are first constructed, the open circuit voltage (OCV) is usually much higher than the equilibrium OCV which is obtained after aging. This is believed due to the self discharge of impurities which are generally associated with the active cathode. For example, in a Li/FeS.sub.2 cell, the initial OCV can be over 3 volts whereupon it will decrease to a level of about 1.8 volts after about a year storage at ambient temperature. Since the nominal OCV level for a Li/FeS.sub.2 cell is generally about 1.5 volts, it would be beneficial if its OCV could be stabilized to about 1.8 volts more rapidly. One approach to reduce the initial high OCV due to the presence of impurities in the cathode is to add a reducing metal additive, such as zinc, to the cathode as is disclosed in U.S. Pat. No. 4,163,829 to Kronenberg. This additive will effectively reduce the high potential impurities thus enabling the OCV or the cell to reach an equilibrium level more rapidly. This rapid attainment of an equilibrium or stable OCV is important in that it allows the cell to be put into use at an earlier date after the manufacture of the cell.
It is, therefore, an object of this invention to provide a nonaqueous lithium cell that has an improved pulse voltage output particularly at low temperatures.
Another object of the present invention is to provide a nonaqueous lithium cell that can reach an equilibrium OCV level rapidly after being manufactured.
Another object of the present invention is to provide a Li/FeS.sub.2 cell that has an improved pulse voltage output particularly at low temperatures and is capable of attaining an equilibrium OCV level rapidly after being manufactured.
Another object of the present invention is to provide a Li/MnO.sub.2 cell that has an improved pulse voltage output particularly at low temperatures and is capable of attaining an equilibrium OCV level rapidly after being manufactured.
Another object of the present invention is to provide a nonaqueous lithium cell with the lithium halide additive to improve the voltage level on pulse discharge of the cell particularly on low temperatures and to decrease the time required for the cell to attain its OCV equilibrium level after being manufactured.
The foregoing and additional objects will become more apparent from the following description.